To diagnose whether a patient is suffering from cancer or has a predisposition, cells need to be sampled from a patient and a thorough analysis of the cell sample is required in order to evaluate whether abnormal or aberrant cells are present. Mainly, a pathologist or other skilled medical personnel will base the diagnosis on specific characteristics of the cells in the sample, such as cell morphology, the presence of certain types of cells or proteins and more. These cytological tests are based on a two-dimensional presentation of the cells present in the sample and mostly require the fixation of cells on a substratum and the use of dyes or stainings to visualize specific features of the cells. This is a time consuming and cumbersome work, and requires well-trained specialists. Moreover, as many of the solutions used to fix and stain the cells, this approach will inevitably lead to loss of cell structures and information stored therein. This might thus interfere with the possibility of a reliable interpretation and diagnosis from the sample. Inadequate processing of a sample may lead to an increased number of false negatives diagnoses. For instance, of the over 50 million cervical cytological PAP smears, which are performed in the USA each year, a high false-negative interpretation rate of 20-40% has been described (Williams et al., 1998), frequently leading to fatal consequences. Most of these false negatives are the result of inadequate sample processing.
Since 1990 many advanced technologies focusing on sampling, smear preparation, or screening quality control have been developed and introduced into the practical work to prevent the false negative rate in screening. These commercial devices can be divided into the following categories based on their approaches: (1) for a better slide preparation to reduce sampling error, such as thin-layered liquid based preparation (ThinPrep™, SurePath, Tripath); (2) for reducing workload and screening error, such as autoscreening system (ThinPrep Imaging System, Cytyc, Boxborough, Mass.) and FocalPoint System (Tripath Imaging, Burlington, N.C.); (3) for laboratory quality control, such as rescreening (Papnet); and (4) for quality assurance, such as proficiency test. However, most of these devices are not designed to assist diagnosis by supplying the calculable parameters to eliminate interpretation errors and inter-observer discrepancy. In addition, it is not applicable for general cytological laboratory because of high cost and technical or linguistic gaps. Thus, without a reproducible and quantitative tool, it is still an unsolved problem for a routine cytological laboratory to improve the diagnostic divergence caused by visual observation.
The Papanicolaou (PAP) smear has been the cornerstone of cervical cancer screening since 1949. By definition, the PAP smear is a stain performed on cells smeared on a slide and visualized by microscopy. Following the advent of liquid-based cervical cytology (LBC), cells from the cervix were obtained using a brush, suspended in a fixative solution, and then applied to a slide prior to staining. Highly trained cytotechnologists and cytopathologists review the stained slides looking for evidence of abnormal cells based on morphological appearances (as indicated in Table 1).
TABLE 1Low grade squamousHigh grade squamousintraepithelialintraepitheliallesion (LSIL)lesion (HSIL)Caviation(Moderate-Marked increase)(Mild increase)N/C* RatioN/C ratioCoarse ChromatinHyperchromasiaHyperchromasiaIrregular Nuclear ContourSingle Abn CellsSyncytial AggregatesPleomorphism*N/C = nuclear to cytoplasmic ratioBecause of the necessity to use slides for the PAP smear, other biomarkers used for cervical cancer screening, especially those used for the molecular detection of HPV DNA, are performed on a separate aliquot of the LBC. Therefore, the throughput is not desirable to accommodate the 60-70 million cervical cytology specimens obtained every year in the US and the 150+ million samples worldwide. Further, molecular techniques performed on a slide are cumbersome and time consuming, characteristics that are not amenable to cervical cancer screening.
Clinically, the PAP smear and HPV testing are used together though they are very disparate technologies. The PAP smear has relatively low sensitivity (50%) and relatively high specificity (90%) for high grade cervical lesions (pre-cervical cancer and cervical cancer). Conversely, HPV DNA testing has high sensitivity (>90%) but low specificity (30%) for high grade cervical lesions (pre-cervical cancer and cervical cancer. These performance characteristics have supported the combined use of these tests for effective cervical cancer screening.
In general, the field of cancer diagnosis is in need for methods and devices that analyses cell samples in a non-destructive, non-detrimental and objective manner. Preferably, a diagnosis is performed on the ‘raw’ sample whereby information is provided on the status of the sample and the cells present without the need for further processing of the cell sample (e.g. centrifuging, cell lysis, etc.). Advantageously, the diagnosis is based on both morphological data and protein expression profiles of said cells.
The latter will undeniably lead to a more reliable diagnosis method as more accurate information will be obtained from the analyzing sample.